The following Catholic registers are available for Rathfarnham Parish at the NLI :
Microfilm P.8972
Rathfarnham Marriages Feb. 5, 1777 - May 19, 1781
Rathfarnham & Crumlin Marriages May 26, 1781 - Nov. 18, 1781
Nov. 17, 1781 - Mar. 4, 1789
Rathfarnham Baptisms Jan. 1, 1777 - May 1781
Rathfarnham & Crumlin Baptisms May 1781 - Nov. 14, 1781
Rathfarnham Baptisms Nov. 18, 1781 - Dec. 1, 1788
(Baptisms and Marriages for 1788-1807 are missing.)
Microfilm P.8972
Rathfarnham (continued) Baptisms Sept. 18, 1807 - Jan. 15, 1832
Marriages Sept. 22, 1807 - Jan. 9, 1832
Baptisms Jan. 22, 1832 - Feb. 1, 1852
Jan. 7, 1861 - Oct. 2, 1864
Marriages Jan. 23, 1832 - Jan. 8, 1852
Nov. 19, 1862 - Nov. 3, 1864
Baptisms Jan. 1, 1852 - Feb. 7, 1857
Marriages Jan. 5, 1852 - Nov. 21, 1858
Baptisms Oct. 9, 1864 - Mar. 24, 1878
Aug. 20, 1857 - Sept. 26, 1858
Marriages Nov. 12, 1864 - Mar. 4, 1878
Baptisms Mar. 31, 1878 - June 27, 1917
Marriages Feb. 12, 1878 - July 24, 1933
I would not usually expect parish registers to contain any more information than the civil register (many that I've seen include quite a bit less detail).
p.s. what was Percy Dunlop's fathers name ? I have located a couple of Dunlop entries close to Rathfarnham in an 1894 trade directory.
Shane